Galvanometer



Junel,1926. 1,587,010 W. R. COLEY GALVANOMETER Filed March 20, 1924' ILWL I [#1 HHHHI A TTORNEY.

Patented June 1, 1926.

UNITED STATES PATENT o.FF1c .f

WALTER B. GOLEY, OF PHILADELPHiEA, PENNSYLVANIA, ASSIGNOB TO LEEDS & NORTERUP COMPANY, PHILADELPHIA, PENNSYLVANIA, A CORPORATION OI PENNSYLVANIA.

GALVANOMETEB.

Application filed March 20, 1924. Serial No. 700,577.

My invention relates to galvanometers, and more particularly of the type havlng a moving system comprising a coil deflecting or rotatable in a magnetic field;

Inaccordance with my invention, the Sensitivity of a galvanometer is increased many told, as of the-order of five to ten fold, by

utilizing magnetic impurity of the moving system, as, for example, a slight amount of magnetic foreign material, such as iron or the like, adhering to or within the movable coil and disposed in the'magnetic field in which the coil moves, to produce a torque opposing the torque of the suspension or mounting of the coil to produceaneflfect equivalent tothe use of a more delicate suspension or mounting for the coil which is finer or weaker than the suspension or mounting actually employed, and thereby efiecting a material increase in the sensitivity and the period of vibration of the moving coil system. I

My invention resides in a method of and meansv for increasing the sensitivity of a galvanometer as hereinafter described and claimed. 1

For an understanding of my method and for an illustration of one of the various forms my structure may take, reference is to be had to the accompanying drawing in which; v

Fig. 1 is a front elevational view of a I galvanometer structure embodying my invention.

- Fig. 2 is a side elevational view, artly vertical section, of thestructure s own in Fig. 1.

Fig. 3 is a rear elevational view 'of the structure shown in Fig. 1. I r

Fig. 4 is a horizontal sectional view taken on the line 4-4 of Fig. 3.

' Fig. 5 is a fragmentary perspective view of a part of, mystructure.

- It has heretofore nometer there has generally been unintentionally present magnetic impurity in the form of minute particle or particles of magnetic foreign material, such as iron or other magnetizable material, which is invisible, or partially-so, to the unaided eye, or which ma be within the coil itself, in its enamel or other insulation, or otherwise in or adherent to the coil. It has been proposed to render magnetic imbeen known that in a movable coil structure of a sensitlve galva wire or conductor of the purity innocuous or, of no efiect by so modifying the magnetic field, as by rendering it radial, that the torque produced by the action of the magnetic field upon the magnetic impurity is reduced to zero, in which case 1,

the natural period of the moving coil system is the same both when disposed in the magnetic field and when removed therefrom.

In accordance with my invention however,

advantage is taken. of the presence of magnetic impurity adhering to or in the coil and disposed in'the magnetic field in which the coil is movable, or socalled magnetic impurity is added to that already present in the movable coil system,.or in the rare cases when no magnetic impurity is present, sufficient is added, and the magnetic field is so modified, adjusted, distorted or controlled that it produces a torque, by its action upon the magnetic impurity, which is caused to oppose the torque exerted upon the moving coil by its filar orother suspension or mounting so that the net torque exerted upon the movmg coil system and opposing the tor ue caused by the current flowingthrough the 0011 while in the magnetic field is materially reduced with the result that the natural period of the moving coil system while in the magnetic field is greatly prolonged or increased, even to the extent of attaining a period three or fourtimes the period of the coil system when removed from the magnetic field, and the sensitivity of the galvanometer is consequently increased to even a greater extent than the increase inthe natural period.

In accordance wlth my invention the sen torque, in practice this is impossible'and the filar or other suspension must be sufficiently rugged to withstand handling and shipping, and this necessarily involves a suspension of greater cross section and eflfectings greater torque notwithstanding such greater crossrllfl section and greater torque of a sufficiently rugged suspension, in accordance with my invention I am enabled to procure extremely high sensitivity by causing the magnetic impurity, present or applied, to exert a torque of suitable magnitude opposing that of the sufliciently rugged suspension. with the resnltequivalent to that obtainable by a far'sm'aller or more delicate suspension.

Referring to the drawing, M is a permanent magnet carried by any suitable support or base, not shown, and exhibiting at its ends, as usual, north and south poles N and S. Carried by the same support or base, or by any other suitable means, is the fixed vertically extending metallic non-magnetic member or plate A carrying at its upper end an adjustable torsion head a to which is attached the upper end of the filar suspension, such as a wire or, as indicated, ribbon b secured at its lower end to the member 6, secured to the rotatable coil 0 in its axis of rotation. Carried by the member 0, or otherwise suitably attached to the coil or its suspension is the usual mirror d, which reflects a spot of light upon a' stationary galvanometer scale, which isgenerally straight, but which may take any other suitable form, as well understood in the galvanometer art., Attached to the coil C at its lower end in its axis of rotation is the lower filar suspension member e attached at its lower end to the post or stud f carried by but insulated from the member A as well understood in the art. Current enters by one of the filar suspension members, as by the poles N and S of the permanent magnet b M are. the rear faces is of the pole pieces m, m, of soft iron or equivalent magnet-izable material detached from magnet M and having the cylindrical or other suitably formed pole faces a, at between which and the core 9 is. formed an annular or equivalent air gap within which is rotatable the .coil C whose axis of rotation is. the filar suspension e. .v I Extending through the slots 0 in the rectangular'portionj'p of the plate A are the screws g, two for and'threadin'g into each of the pole pieces m, thereby holding and supportingthe' pole piecesjm to and upon the member A, to permittheir adjustment la sml y, rie cd n. sts-J1 an 'fh with respect to' theice'il O,'while maintaining coside faces 25 of the portion p of the plate" A, whereby rotatable adjustment of the screws .9 will with great nicety determine the lateral adjustment of the pole piece m toward or away from the coil C, the pole piece being detached from but remaining in operative relation with the pole of the magnet M.

By so adjusting either or both of the pole pieces m, the magnetic field between the pole pieces m, m and in which thecoil C with its magnetic impurity is located, the magnetic field is so modified, distorted, directed or controlled that the torque caused by the action of the magnetic field upon the magnetic impurity is caused to have such magnitude and to act in'such sense or direction as to oppose the torque caused by or due to the filar suspension 5, e, or its equivalent, with the result that the net torque exerted upon or by the coil C in opposition to the torque caused by reaction between the magnetic field and the current traversing the;

conductor of which the coil C is Wound, is greatly reduced, yielding markedly increased sensitivity which could otherwise be attained only by use of much finer or much more delicate suspension. The effect v of, the torque due to magnetic impurity is, as aforesaid, greatly to increase the natural period of oscillation or vibration of the coil C or the oscillatory system of which it is a part, and its natural period may be in creased to three or four fold the natural period which the coil system has when removed from the magnetic field, with the result that the sensitivity "is greatly 1n- .creased, and so securing a sensitivity five to ten times the maximum sensitivity heretofore obtainable. so far as I am aware, with structure the same as regards shape, size and number of turns of coil, and as regards the suspension and the torque exerted there- 'cated practically anywhere thereon, as at either end or, and preferably, at eitherver t'icalside, is acted upon by a modified or non-uniform field effecting a torqueupon the coil. The direction of adjustment of a pole piece is that which causes the torque exerted by the magnetic material of or on the} coil to oppose the torque exerted upon the'coil by its suspension, with resultant in-' y In the example illustrated, the magnetic crease in sensitivity and natu'ralperiod of and magnetic material is small and tends toward zero.

' While the torque exerted by the coil sus pension bears a linear relation to the angular' displacement of the coil from zero or normal position, the opposing torque effected bythe magnetic impurlties varies in accordance with a. trigonometric function, as the cosine, of the angle between the direction of the magnetic field and the direction of motion ofjthe coil. In consequence there is a tendency to disturb thelinear relation betweenstrength of current traversing the coil C and the angular displacement of the coiL. This however is not serious for small angu-. lar' displacement of the coil, and is partly corrected because the beam of light reflected from the mirror 03 on to a straight scale is affected by a tangent law. However, when the galvanometer is used in so called null methods, or under circumstances where the angular deflections of the coil system from zero are small, the aforesaid variation from linear relatlon 1s inconsequential.

' What I claim is:

1. The method of decreasing the torque 1 exerted by its suspension upon a galvanome- "ter coil deflecting in a magnetic field which comprises modifying the magnetic field in which the coil moves to efiect upon the coil in opposition to the torque of the suspension a torque due to the action of said magnetic field upon magnetic material disposed in said field and controlled by said suspens1on.

2. The method of increasing the sensitivity of a galvanometer comprising a coil deflecting, when traversed by current, in a magnetic'fieldin opposition to a coil-control ling torque which comprises modifying saidmagnetlc field to produce a torque opposing 'said coil-controlling torque by the action of i said magnetic, field upon magnetic material disposed in said field and movable therein with said coil. I

3; The method of increasing the sensitiviity of a galvanometer comprising a coil defleet ng, when traversed by current, -in a magnetic field in opposition to a coil-controlling torque-which' comprises modifying said magnetic field to produce a torque opposing said coil-controlling torque by the action of saidfield upon magnetic impurity oflsaid coil. I 3

4. The combination'witha galvanometer comprising a coil deflecting in a magnetic field when traversed by current, and means producing a torque opposing deflection of said coil, of magnetic'material disposed in said field and movable with said coil, and

said coil, of magnetic material disposed in 4 'said field and movable with said coil, and means for modifying said magnetic field to produce by the action of said field upon said magnetic material a torque opposing the torque produced by said means.

6. The combination with a galvanometer comprising a coil having magnetic impurity and deflecting in a magnetic field when traversed by current, -and means producing, a torque opposing deflection of said coil, of adjustable means for modifying said field to effect by the action thereof upon said impurl'ity a torque afi'ecting deflection of said 001 7 The combination with a'galvanometer comprising a coil having magnetic impurity and deflecting-in a magnetic field when traversed by current, and means producing a torque opposlng deflection of said coil, of

. adjustable means for modifying said field to effect by the action thereof upon said impurity a torque opposing the torque pro ducedby said means.

8. The combination with a galvanometer comprising a coil having magnetic impurity and deflecting in a magnetic field when traversed by current, and means producing a tude greater than the period due to said torque producing means.

9. In combination with a, galvanometer comprising a coil, a magnet having pole piece structure for producing a field in which said coil deflects when traversed by current,-

and means producing torque opposing deflection of said coil, Ofmagnetic material disposed in said field and movable therein with said coil, and means for effecting adjustment of said pole piece'structurewith respect to said magnetic material for effecting a coil-controlling torque due to the actiorli of said field upon said magnetic mater1a 10. In combination with a galvanometer comprising a coil, a magnet having pole piece structure for producing a field in which said coil deflects when traversed by 11. The combination with a galvanometer comprising a coil having magnetic impurity, a magnet having pole piece structure for producing a magnetic field in which said coil deflects when traversed by current, and a coil suspension opposing its deflection, of means for effecting adjustment of said pole piece structure for procuring by the action of said field upon said impurity a coil-controlling torque.

12. The combination with a galvanometer comprising a coil having magnetic impurity, a magnet having pole piece structure for producing a magnetic field in which said coil deflects when traversed by current, and a coil suspension opposing its deflection, of means for effecting adjustment of said pole piece structure for procuring by the action of said field upon said impurity a torque opposing the torque exerted by said suspension.

13. The combination with a galvanometer comprising apermanent magnet, pole pieces therefor detached therefrom, a coil deflecting when traversed by current in the magnetic field between said pole pieces, means producing torque opposing deflection of said coil, and means for varying the sensitivity comprising magnetic material disposed in said field and movable with respect to said ,magnet and said pole pieces for producing by the action of said field as modified by said pole pieces upon said magnetic material a torque acting upon said coil.

15 The combination with a galvanometer comprising a permanent magnet, pole pieces therefor detached therefrom, a coil deflecting when traversed by current in the magnetic field between said pole pieces, means producing torque opposing deflection of said coil, and means for varying the sensitivity comprising magnetic material disposed in said field and movable with said coil, and means for adjusting a pole piece with respect to said magnet and said magnetic material for producing by the action of said field upon said magnetic material a torque opposing the torque produced by said means.

15. The combination with a galvanometer comprising a permanent magnet, pole pieces therefor detached therefrom, a coil having magnetic impurity and deflecting in the field between said pole pieces when traversed by g current, and means producing torque oppos ing deflection of said coil, of means for increasing the sensitivity. comprising means for adjusting said pole pieces to distort said magnetic field'to effect by its action upon said magnetic impurity a torque opposing the torque produced by said means.

16. A galvanometer comprising a magnet,

pole pieces therefor, a'core disposed in the magnetic field between said pole pieces, a. coil and magnetic material movable therewith in the field between said pole pieces and core, a member supporting said pole pieces in detached relation to said, magnet, a coil suspension carried by said member, and means for adjusting at least one of said pole pieces with respect to said member.

17. A galvanometer comprising a magnet, pole pieces therefor, a core disposed in the magnetic field between said pole pieces, a coil having magnetic impurity and movable in the field between said pole pieces and core, a member supporting saidpole pieces in detached relation to said magnet, a coil suspension carried by said member, and means for adjusting at least one of said pole pieces with respect tosaid member.

18. A galvanometer comprising a magnet, pole pieces therefor, a supporting member, a 'core carried by said supporting member and disposed between said pole pieces, a coil movable in the field between said pole pieces and core, a suspension for-said coil carried by said supporting member, said coil having magnetic impurity, said pole pieces carried by said supporting member in detached relation to said magnet, and means for adjusting each of said pole pieces with respect to said supporting member for distorting said field to effect by the action of said field upon said impurity a. torque in opposition to said suspension.

19. A galvanometer comprising a permanent'magnet having plane pole faces, pole pieces, each having faces coacting respectively with said face of said supportlng member and with one of said ole faces of said magnet, a core disposed etween said pole pieces and supported by said supporting member, a coil having magnet1c 1mpurity disposed. inthe field between sald pole pieces and said core, a suspension for sald coil carried by said supporting member, and a screw threaded in each of said pole pieces and adapted to engage said supporting member for effecting adjustment of the pole piece to distort the magnetic field to produce by its action upon said magnetic impur1ty a torque opposing the torque produced by said suspension.

WALTER R. COLEY. 

